Delaminated or exfoliated cation exchanging layered materials (such as delaminated 2:1 layered silicate clays) can be used as a reinforcing filler in a polymer system. Such polymer systems are known as “nanocomposites” when at least one dimension of the delaminated cation exchanging layered material is less than sixty nanometers. Nanocomposite polymers generally have enhanced mechanical property characteristics vs. conventionally filled polymers. For example, nanocomposite polymers can provide both increased modulus and increased impact toughness, a combination of mechanical properties that is not usually obtained using conventional fillers.
Ideally, the degree of delamination of the cation exchanging layered material in a nanocomposite is such that only single layer units of the cation exchanging layered material are present. However, a significant enhancement in the physical properties of a polymer are often observed when two, three, four and more than four layer units are observed in a nanocomposite. Typically, the thickness of a single layer of a delaminated cation exchanging layered material is in the range of one or two nanometers while the length and width of such layer can be in the range of, for example, one hundred to one thousand nanometers. If the cation exchanging layered material is not delaminated in the polymer, then the mechanical property improvement of the polymer composite will usually be no better than if a conventional micron sized filler is dispersed in the polymer.
Cation exchanging layered materials are often treated with an organic cation (usually an “onium”) to facilitate delamination of the cation exchanging layered material when it is blended with a polymer (see, for example U.S. Pat. No. 5,973,053). Conventionally, the layered material is “fully exchanged” or “overexchanged”, i.e., the exchangeable cations of the layered material are essentially fully replaced by onium ions or the exchangeable cations of the layered material are essentially fully replaced by onium ions and the material contains additional onium ions.
Recent developments have been made using less than fully exchanged cation exchanging layered material. Pinnavaia et al. (U.S. Pat. No. 5,993,769) disclosed a 2:1 layered silicate clay composition wherein a portion of the cation exchange capacity of the clay was satisfied by an organic onium cation with the remainder of the cation exchange capacity of the clay being satisfied by an inorganic cation, the composition being “homostructured” and not randomly interstratified, regularly interstratified, phase segregated or entrapped. Pinnavaia et al. distinguished their homostructured composition from the randomly interstratified, regularly interstratified, phase segregated and entrapped compositions by the distinctive x-ray diffraction pattern of the homostructured composition, see FIGS. 1A to 1E and FIG. 2 of Pinnavaia et al.
Pinnavaia et al. asserted that their homostructured compositions were superior to the prior art randomly interstratified, regularly interstratified, phase segregated and entrapped compositions.